1. Field of the Invention
The present invention relates to an anti-counterfeit medium and a verification method.
2. Description of the Related Art
Media used as securities such as banknotes and merchandise coupons or certificates such as passports conventionally utilize a device difficult to counterfeit (to be referred to as an anti-counterfeit device hereinafter) for the purpose of preventing counterfeit. Anti-counterfeit technologies include an overt technology and a covert technology. In the overt technology, authenticity is determined by observation with the unaided eye. On the other hand, in the covert technology, authenticity is determined using a verification tool.
The overt technology has the advantage of obviating the need for a verification tool for authenticity determination. Simultaneously, the overt technology is disadvantageous because it is easy to notice the anti-counterfeit technology employed in the anti-counterfeit device.
Some of the recent anti-counterfeit devices use a latent image to be visualized upon observation through a polarizer to prevent counterfeit. For example, Jpn. Pat. Appln. KOKAI Publication No. 2005-326882 describes using a device including a reflecting layer and a birefringent layer formed by cross-linking a liquid crystal monomer to prevent counterfeit of banknotes. In this anti-counterfeit device, the birefringent layer includes two regions whose slow axis directions differ by 45°. These regions form latent images that cannot be discriminated from each other upon observation by the unaided eye and are visualized by observing reflected light through a polarizer.
In this technique, a polarizer is used as a verification tool. In the anti-counterfeit technology using a verification tool, for example, the above-described anti-counterfeit label is pasted on each authentic tradable coupon or ticket. The retailer or service company prepares the verification tool in advance. This allows the retailer or service company to determine the authenticity of tradable coupons or tickets received from general consumers using the verification tool.
However, the general consumers normally have no verification tool. Hence, in the above-described technique, the general consumers can hardly determine the authenticity by themselves.
Jpn. PCT National Publication No. 2001-525080 describes a medium in which a flexible support member having optical transparency supports both an anti-counterfeit device and a verification tool.
In this medium, the anti-counterfeit device includes a birefringent layer facing a part of the support member, and a linear polarizer serving as a first polarizer intervening between them. The birefringent layer is formed by cross-linking a liquid crystal monomer, and includes two regions whose slow axis directions differ by 45°. These regions form latent images that cannot be discriminated from each other upon observation by the unaided eye.
In this medium, the verification tool is a second polarizer facing a part of the support member. When the support member is bent to make the birefringent layer intervene between the first polarizer and the second polarizer, and transmitted light is observed in this state, the latent images are visualized.